Harmonic suppression in goniometers



May 5, 1959 K.v BAUR HARMoNIc SUPPRESSION 1N GoNIoMETERs :s 'Sheets-sheet 2 Filed May e, 1957 May 5,- 1959 y v. y"K.V.BAUR '2,885,672

' HARMONIC SUPPRESSION-IN GoNIOT/PETERSl Filed May 6, 1957 5 lSheets-SheetA 3 8a /Ob 0 a u [2b 0 4 lsb" Fig. 4

. mvENToR KARL BAUR PATENT AGENT United States PatentOce Y2,885,672 Patented vMay 5, 1959 2,885,672 l HRMONIC SUPPRESSION IN GONIOMETERS Krl Baur, Ulm (Danube), Germany, assigner to Telefunken G.m.b.H., Berlin, Germany The present invention relates to improvements in goniometers and, particularly, to those in which harmonics of the fundamental frequency caused by a nonsinusoidal composite coupling characteristic between the rotor coil and the stator coils may be cancelled out.

The invention contemplates the subdivision of the rotor coil or each of the stator coils into a plurality of coil sections which are connected either in series and/or parallel, and wherein these coil sections are disposed at such angles with respect to each other that the elfective components of the harmonics to be eliminated are mutually cancelled.

It has been known that the composite curve of the coupling coefficient between the stator coils and the rotor coil of a goniometer deviates from an ideal sinusoidal pattern because the magnetic eld by which the rotor coil is coupled is not homogeneous. A homogeneous magnetic eld and, therefore, a sinusoidal coupling can only be obtained theoretically, i.e., by providing stator coils of infinite lengths. The curve of the composite coupling coefficient which deviates from a sine wave can be mathematically represented by a Fourier analysis and by superposition on a sine wave, one cycle of which is covered by turning of the rotor coil 360 of the sine wave corresponding with the harmonic of the fundamental wave. In order to clarify the terms for harmonics, higher harmonics, and their ordinal numbers, the following is offered to explain how the ordinal numbers of the harmonics are to be counted. The rst harmonic will be called the fundamental wave, while cycles of the second,

third, etc., harmonics will be 1/2 as long, 1/a as long, etc., as one cycle of the rst harmonic, i.e., of the fundamental wave. Thus, the fundamental and harmonics may be represented as n=1; n=2; n=3, etc.

In the case of a symmetrical design for the goniometer, a condition which will be fulfilled in practice, all evennumbered harmonics are eliminated. A further improved curve of the coupling coeicient can be obtained by eliminating especially undesirable odd-numbered harmonics in the antenna, by using more than two directional loops or, in case of an Adcock installation, by using more than four Adcock antennas. As a result of this, all those harmonics are eliminated from the coupling coefficient curve, the ordinal numbers of which are equal to the number of directional loops of the multiple antenna system or, are equal to half of the number of Adcock antennas or a multiple thereof. If, for example, a six-mast Adcock antenna system is used, the third harmonic and all multiples thereof, ie., the sixth, ninth, twelfth, etc., are eliminated. f

f lt has ralso been known to eliminate any harmonic of the composite non-sinusoidal coupling coecient curve between stator coils and rotor coil of a goniometer by dividing either the rotor coil or each of the stator coils into two equal coil sections forming an angle therebetween of such size, that the components of the harmonic to be eliminated are cancelled in the rotor coil. The two coil sections of the stator coils or the rotor coil are either arranged in series or in parallel. By such arrangement of the stator or rotor coils, also multiples of the eliminated harmonics are cancelled.

It is possible, by combining the three known systems mentioned in the foregoing at the same time, i.e., by using a multiple antenna system, the division of the stator coils and the division of the rotor coil, to eliminate three harmonics as well as the multiples thereof from the composite coupling coeflicient curve. However, other harmonics may become more pronounced, due to the division of the coils, so that a pure sinusoidal curve cannot be obtained by applying the known systems.

It is an object of the present invention to cancel any harmonic from the non-sinusoidal coupling coefficient curve between the stator coils and the rotor coil in a goniometer, so that the coupling has a substantially purel sinusoidal curve which is a function of the displacement angle of the rotor coil, whereby the action of the higher harmonics decreases with increasing ordinal number and can be neglected above a certain harmonic.

It is a primary object of the invention to subdivide the coil sections of the rotor or the stator once or several times to provide further coil sections which will eliminate further harmonics and to angularly displace these further coil sections obtained by such division, said sections being connected either in series and/or in parallel, in

such as manner that the components of the harmonics to be eliminated cancel out in the rotor or stator coil sections.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since4 various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawings:

Figure l shows an iron core for a six-mast Adcock antenna system;

Figure 2 is a diagram, illustrating how cancellation of the fth and seventh harmonics is obtained by subdividing the rotor coil in the goniometer according to Figure 1; Figure 3 shows an air-core goniometer according to the invention;

Figure 4 shows a device similar to that shown in Figure l. except that extra windings have been added to make the goniometer into a coordinate transformer.

Each of the stator coils 1 to 6 in the goniometer of Figure 1 is fed from a different mast of a six-mast Adcock antenna system. These coils are wound on an annulary core 7 which may be made of iron or of ferrite. A rotor' 8 is disposed in the center of the annular core 7, said rotor being made also of iron or ferrite. 8 is rotatably mounted on an axis 9 and serves as a coil supporting body for the rotor coil which, in the' present case, is divided into four coil sections to cancel out two harmonics of the coupling coeiicient curve. For the sake of clarity, the individual coil sections are indicated in Figure l only by full or dash-dash lines, such showing, however, is not intended to indicate only one harmonic of the coupling coeiiicient curve is to be eliminated in the rotor coil, it would be suiiicient to divide this coil into two equal sections 10 and 11, forming an angle 61, wherein goniometer, for example,

The rotor' where n is the ordinal number of the harmonic to be eliminated. If, for example, the fth harmonic is to be eliminated, then and amounts to 25.7 for eliminating the seventh harmonic. All of the individual coil sections may be arranged either in series or in parallel. However, it is possible to provide groups of coil sections in series and to connect such groups in parallel, or vice versa.

Thus, in the goniometer according to Figure 1, all of the harmonics of the coupling coefficient curve up to and including the tenth harmonic are eliminated because, as already mentioned, even-numbered harmonics are eliminated due to the symmetrical construction of the goniometer, the third harmonic and its multiples are eliminated by the use of a six-mast Adcock antenna system and, finally, the fifth and seventh harmonics are cancelled by the division of the rotor coil according to the present invention. Other harmonics, for example, the eleventh and thirteenth, which are still present, can be cancelled by further subdivision of the rotor coil or of the individual stator coils. However, a system as shown in Figure l is adequate for practical harmonic cancellation, because the amplitudes ofthe eleventh and thirteenth harmonics are very small.

The diagram of Figure 2 illustrates how cancellation of the fifth and seventh harmonics is obtained by dividing the rotor coil of a goniometer, according to Figure l. The coupling coeicient k is plotted on the ordinate as a function of the displacement angle of the rotor coil plotted on the abscissa. 14 denotes a portion of one cycle of an ideal sinusoidal curve of the coupling coefcient. As mentioned in connection with Fig. 1, there occurs, in addition to the fundamental wave, i.e., the rst harmonic, harmonics of other ordinal numbers, namely, the fth harmonic, denoted by 15, and the seventh harmonic, denoted by 16, so that the coupling coefficient follows a composite curve 17. The amplitudes of the harmonics are Vshown exaggerated in the diagram of Figure 2, in order to better illustrate the cancellation. Actually, the values of the amplitudes are only a fraction of the amplitudes of the fundamental, so that the coupling coeicient curve does not actually deviate to as large an extent as shown in Figure 2 from the sine curve of the fundamental wave. Corresponding to the angular displacements of the coil sections through 13, vertical lines 10', 11', 12 and 13' are shown on the diagram of Figure 2, said lines corresponding to the angular positions of the individual coil sections 10 through 13 of Figure l. For any position of the rotor coil, there exist magnitudes a, ci', b, b; c, c; and d, d', which indicate quantitatively the components of voltages of the fifth and seventh harmonics which appear in the individual coil sections 10 through 13. If, for example, it is assumed that the coil sections 10 through 13 are connected in series, the voltages which are proportional to the lengths a, a d, d', are cancelled at the output of the rotor coils because a=a d=d, wherein the prime values have the opposite sign from the non-prime values.

The air-core goniometer shown in Figure 3 is suited to be connected to a crossed-loop antenna. The rotor coil is subdivided several times to obtain cancellation of three harmonics of the non-sinusoidal coupling coecient curve between the stator coils and the rotor coil. The two stator coils 18 and 19 are shown partially interrupted on their upper sides, so that the arrangement and division of the rotor coil will be clearly visible. Each of the ends 20, 20 of the stator coil 18, and each of the ends 21, 21 of the stator coil 19 is connected to a terminal of a directional antenna loop. A cylindrical rotor body 22 is provided within the stator coil, said body being rotatably mounted about an axis 23. This rotor body 22, which may be made of insulating material, carries the rotor coil. In order to eliminate a harmonic, the rotor coil is divided into two equal sections, said sections forming an angle 61, selected in such manner, that the components of the harmonics to be eliminated are cancelled out in the rotor coil, said components being disposed in the directions of the full lines 24 and 25 in Figure 3. If, for example, the third harmonic is to be eliminated, the

The cancellation is based upon the fact that, for example, at a certain position, one half of the rotor coil is coupled with a maximum, while the other coil half is coupled with an opposite maximum of the third harmonic, SO that the components of the third harmonic are cancelled out at the output of the rotor coil. In order to eliminate another harmonic, for example, the fth harmonic, the sections represented by the lines 24 and 25 have to be subdivided and these sections are then arranged along and represented by the dash-dash lines 26 and 27. These latter lines are displaced with respect to the lines 24 and 25 by an angle 62 which amounts to when the fth harmonic is to be eliminated. The coil sections would have to be further subdivided from the positions 24, 25, 26 and 27 to cancel out a further harmonic, and these sections would be arranged along the dash-dash lines 28 through 31. The latter lines are displaced with respect to the lines 24 through 27 by au angle 63 which amounts to for the elimination of the seventh harmonic. Other, higher harmonics n can be eliminated in an analogous manner. The coil sections present in the individual cases have to be further subdivided to cancel out the next higher harmonic n', and the divided coil sections have to be displaced by an angle calculated as where n is the ordinal number of the harmonic to be eliminated in any individual case. It is noted that, first, the harmonic with the lowest ordinal number, and then the next harmonic of the next higher ordinal number have to be cancelled in order. In other words, the angles and etc. are to be made smaller with each higher harmonic. The individual coil sections to be arranged along the lines 24 through 31 are omitted in Figure 3 for the sake of clarity. The individual coil sections may obviously comprise one or several coils or turns according to the given requirements.

Figures 1 and 3 show goniometers in which the cancellation of undesired harmonics of the coupling coefiicient curve is obtained by multiple division of the rotor coil. However, by multiple division of the stator coils, a similar cancellation of the harmonics can be obtained in an analogous manner, the individual sections of the stator coil being displaced with respect to one another in such a manner, that they form an angle with the axis of rotation of the rotor as its apex, whereby this angle is to be calculated in an analogous manner, as in case of div-ision of the rotor coil, as follows:

Since a goniometer has at least two stator coils, and in many cases more than two, it often is necessary, in cases of multiple subdivision of the stator coil, to wind coil sections assigned to diierent stator coils one upon each other, so as to cancel out several harmonics. The operation of the goniometer according to the invention is not impaired by overlapping of the winding zones of the various coils. If a great number of harmonics is to be eliminated, it is recommended to simultaneou-sly provide a multiple subdivision of the rotor coil and of the stator coils.

The invention can be applied in the same manner to coordinate transformers which are generally constructed similarly to iron-core goniometers, the stator coils 1, 2, 3, 4, 5 and 6 of which are adapted to be connected to more than four Adcock antennas or to more than two directional loops. In such a coordinate transformer (Figure 4), parts corresponding with those in Figure l have been given similar reference characters, but a stationary core 8a is substituted in place of the rotor 8, and two similar sets of secondary coils 10a, 11a, 12a, 13a and 10b, 11b, 12b, 13b are wound on said stationary core 8a, corresponding coils being displaced 90. While the stator coils 1, 2, 3, 4, 5, and 6 of the coordinate transformer are connected with the individual antennas of a multiple antenna system (not shown), as in a conventional goniometer, the outputs of the secondary coils may be connected With the dellection plates of a cathode ray tube via an amplifier (not shown), said tube serving to indicate the resultant angular bearing. The stator coils and the secondary coils of such coordinate transformers may be subdivided in accordance with the invention. As in the case of the subdivided stator coils, the winding zones of two coils may overlap in the secondary coils of a coordinate transformer.

In some constructions of goniometers according to the invention, undesirable coupling capacities may occur, due to the subdivision of stator and/or rotor coils, wherein such coupling capacities result in deviations from the sinusoidal coupling coeicient curve between stator and rotor coils. Such coupling capacities occur, for example, if the rotor coil is subdivided several times according to the invention, and if a second coil, for example, an auxiliary coil for the sense direction finding is provided on the rotor core perpendicular with respect to the rotor coil, because in this case, the outer turns of the subdivided rotor coil are close to the turns of the auxiliary coil. In order to keep these coupling capacities small, it is recommended that ferrite be used as a core for the goniometer coils. Ferrite has a high permeability, so that a required minimum coupling between stator and rotor coils can be obtained with a few turns per coil and with small dimensions, with the result that the coupling capacities may be decreased.

I claim:

1. In a goniometer having rotor and stator coils mutually coupled by a composite coefficient of coupling represented by a cyclic curve deviating from a sine wave to the extent of superimposed harmonic coupling coefficient curves, and at least one of said coils being divided into two sections mutually connected and disposed at such an angle between the sections about the axis of the goniometer as to cancel out the components in said sections attributable to one harmonic and its multiples, the improvement comprising the subdivision of at least one of said coils into further coil sections mutually displaced by an angle about the axis of the goniometer and Isymmetrically arranged with respect to the locus of the center of symmetry of the subdivided coil to cancel the nth harmonic and its multiples from said further coil sections, the angle being equal to l/n.

2. In a goniorneter as set forth in claim 1, the improvernent comprising the subdivision of said rotor coil into two further sections to cancel the nth harmonic and multiples, where n is an odd number different from unity and said further sections are mutually disposed about said axis atan angle of degrees.

3. In a goniometer as set forth in claim 2, said further sections of the rotor coil being additionally subdivided into additional pairs of sections, the sections of each pair being symmetrically disposed with respect to the locus of symmetry of one of said further sections and the sections of each additional pair being displaced from one another by `an angle which is equal to /n, where n is an odd integer different from n and ditferent from unity.

4. In a gonicrneter as set forth in claim 1, the irnprovement comprising the subdivision of said stator coil into two further sections to cancel the nth harmonic and multiples, where n is an odd number diffe-rent from unity and said further sections are mutually disposed about said axis at an angle of degrees.

5. In a goniometer as set forth in claim 2, said further sections of the stator coil being additionally subdivided into additional pairs of sections, the sections of each pair being symmetrically disposed with respect to the locus of symmetry of one of said further sections and the sections of each additional pair being displaced from one another by an angle which is equal to 180/n, where n' is an odd integer dilferent from n and dilferent from unity.

6. In a goniometer as set forth in claim 1, said rotor and stator coils being wound on cores of ferrite.

7. In a goniometer as set forth in claim 1, said rotor coils comprising two similar sets of fcoils, the Coils of one set being respectively disposed at right angles to the corresponding coils of the other set, the coils of said sets being subdivided into Isaid sections displaced by said angle and said rotor and stator coils being oriented and fixed with respect to each other to form a coordinate transformer.

References Cited in the le of this patent UNITED STATES PATENTS 2,282,060 James et al. May 5, 1942 2,305,257 James et al. Dec. 5, 1942 2,600,473 Broekman June 17, 1952 

